Determination of fatty acid methyl esters in cosmetic castor oils by flow injection–electrospray ionization–high‐resolution mass spectrometry

Objective The goal of this work was to set up a high throughput procedure for the determination of fatty acid methyl esters (FAMEs) in cosmetic castor oils using flow injection–electrospray ionization–high‐resolution mass spectrometry, and to demonstrate the need of such analysis for the quality control purposes. Methods The sample aliquot was mixed with isooctane:chloroform (1:1) and submitted to transesterification; the obtained FAMEs were appropriately diluted using water:isopropanol:acetonitrile (20:50:30) with addition of sodium formate which served as an internal standard, lock mass calibrant and promoted the formation of sodium adducts during electrospray ionization (ESI). The principle of flow injection analysis (FIA) was applied for sample introduction to an ESI–quadrupole–time of flight mass spectrometer (ESI‐QTOFMS). The carrier solution was composed of water:isopropanol:acetonitrile (20:50:30). From the acquired MS data, flowgrams of the extracted [M+Na]+ ions were obtained using the following m/z values for individual FAMEs: 293.2451 (C16:0); 315.2295 (C18:3); 317.2451 (C18:2); 319.2608 (C18:1); 321.2764 (C18:0); 335.2557 (C18:1,OH); 349.3077 (C20:0); 377.3390 (C22:0) and m/z 226.9515 for IS. Baseline‐subtracted and filtered signals were integrated, and the list of peaks intensities was exported to Excel, where calibration functions were obtained and quantification carried out. Gas chromatography with a flame ionization detector (GC‐FID) was used as an alternative analytical tool. Results The calibration detection limits for FAMEs of unsaturated fatty acids were in the range 3.61–8.62 μg L−1 and for saturated compounds in the range 8.51–82.4 μg L−1. The results obtained for commercial oils were in good agreement with GC‐FID data; among nine cosmetic oils analysed, three contained low concentrations of ricinoleic acid (C18:1, OH), indicating adulteration of castor bean oil with other vegetable oils. Conclusion Application of FIA for the sample introduction to ESI‐QTOFMS enabled for reliable determination of FAMEs in cosmetic oils with sampling frequency of thirty per hour as compared to two samples per hour achievable using GC‐FID. The proposed procedure is especially well suited for FAMEs of unsaturated fatty acids that are primary components of castor triacylglycerides and contribute to desirable properties of any cosmetic oil. The principle of Flow Injection Analysis has been applied for sample introduction to ESI source of the high resoluti